Much is known of ribosome functions in terms of individual steps in protein synthesis. What is not known is the structure of the ribosome and the functions of the individual components, particularly the RNAs. Our laboratory in the past has investigated the structure-function relationships of Escherichia coli ribosomes and the interaction with aminoglycoside antibiotics, principally by the use of chemical and enzymatic modification techniques. Our investigations and work by others on the structure and function of S5 RNA have led us to propose the following: The S5 RNA has a region, 3' AAG44 5', available for binding tRNAs by complementary base pairing to 5' T psi C 3' of tRNAs, that is only exposed when ribosomes have entered into an initiation complex and have the P site occupied. With the use of the reagent kethoxal (specific for single-stranded guanine residues), we plan to test whether a specific SsRNA-tRNA interaction can take place by determining whether G44 is exposed with ribosomes complexes in initiation. We plan also to analyze the functions of S23 and S16 RNAs by chemical modification of these molecules, and testing activities in reconstituted ribosomes. Past modification studies with nucleases have indicated that some rRNA regions may not function in the process of protein synthesis, although a small segment of S16 RNA has recently been shown to be involved in protein synthesis initiation. Further studies of chemical modification with specific RNA sites blocked may reveal whether certain regions of rRNA are or are not functional during protein synthesis. At the present time it is unclear whether RNA or proteins of the ribosome bind streptomycin. With the use of synthetic double-stranded polynucleotides and natural RNAs, we plan to study the interaction of streptomycin with these polymers. Recently we have found a specific interaction of streptomycin with denaturation of the duplex molecule poly(G) poly(C). Thermal denaturation properties, C14 streptomycin binding studies and streptomycin photoaffinity probes will be used to further investigate the interaction with RNA. We have also found kethoxal to be a very useful reagent to study changes in ribosome structure, since it binds to both ribosomal RNA and protein. We plan to investigate changes produced in accessibility to chemical modification of ribosomes by aminoglycoside antibiotics such as streptomycin, kanamycin and tobramycin.